This invention relates to a high speed data transmission method and the corresponding transmission/reception devices. More specifically, the invention describes a technical solution for digital transmission between two devices in bidirectional and simultaneous manner (full duplex) using only one active wire. The invention makes it possible to achieve high transmission speeds (several dozens of Mbits/sec) with a distance between the devices of up to one meter with comfortable immunity to noise.
The technology described according to the invention may be used in combination with the Recommendation TS102.613 of ETSI (European Telecommunication Standardization Institute) relating to SWP (Single Wire Protocol) and may as an example only be activated after a SIM card and an NFC controller discover their ability to operate in this more efficient mode allowed by the invention. Even though the invention may thus be used in SWP SIM cards, it may also be used advantageously in all environments that require the implementation of digital transmission between two devices in a bidirectional and simultaneous manner (full duplex) using only one active wire, such as for example in the case where the number of contacts available for the components is limited.
Many modulation techniques are in existence for sharing a medium of transmission between two transmission/reception devices, the main ones of which are:
Time-division multiplexing. The two transmission/reception devices transmit in half duplex mode and send their respective data at different times. The granularity of the data sent may vary from the size of a bit to the size of a byte or even a frame. Ethernet, USB, CAN, VAN, LIN or GSM networks use this principle.
Frequency-division multiplexing. Each transmission/reception device occupies a different frequency band. The technology of modems such as those used for ADSL networks use this principle.
Domain division. Each transmission/reception device modulates different physical quantities. The standard TS102.613 (SWP) applies this method, where one of the transmission/reception devices modulates the voltage of a signal whilst the other device modulates the current of a signal.                Sharing by summation. The medium transports the sum of the information transmitted by the transmission/reception devices. The transmission/reception devices deduct the received information by subtracting their transmitted data from the data transmitted through the medium. That function is carried out by a duplexer and is commonly used in conventional telephony systems.        
All these technologies can use a single active communication wire (single ended) or work on a differential pair to increase their immunity to noise in difficult environments (e.g. manufacturing workshops, automobiles etc.)
Half-duplex transmission of data through a communication medium with excessively high granularity can generate high latencies that can harm performance. The effective bandwidth is directly affected by the transmission latency. In order to cancel that side effect, the use of full-duplex technology in combination with an appropriate protocol such as those based on sliding windows, the best known representative of which is HDLC (ISO 13239), is desired.
The issue addressed by this invention is the following:                The solution must have the characteristics of full-duplex communication with interchange granularity of a bit in order to achieve minimum latency,        The solution must be symmetrical and balanced, that is to say that neither of the transmission/reception devices is more privileged than the other (no master or slave),        The solution must make it possible to provide a power saving mode when no application data are transmitted between the two transmission/reception devices,        The solution must supply a procedure enabling one or both of the transmission/reception devices to exit the power saving mode in minimum time, and        The solution must allow an operational distance of at least a meter and a binary speed of up to 100 Mbits/s in a noisy environment.        
The existing technologies described above partly meet the criteria set out above and the closest technology is that of SWP standardised by ETSI with the exception of the transmission speed and operating distance performance. SWP technology can reach 1.6 Mbits/s over a distance of about twenty centimeters.
The invention is aimed at meeting all those technical constraints. To that end, a method for the transmission using the half-duplex mode of a data signal from a first transmission/reception device to a second transmission/reception device, called the remote device, comprising a logical coding step during which at least two distinct transmission times are associated with two respective statuses of the data signal to transmit, is characterised in that it comprises the generation by the first device of a signal including, for the transmission of the signal status, more or less exclusively a plateau at a first voltage level for the time defined by the transmission time associated with the status to transmit and a falling edge, to the exclusion of any rising edge, the transmission of a data signal status from the second device to the first one comprising the generation of a signal by the second device comprising more or less exclusively a plateau at a second voltage level and a rising edge, to the exclusion of any falling edge. The signal status may be a binary status, “1” or “0” or a sequence of bits, e.g. “101”.
The invention uses this “new type of multiplexing” to achieve a full-duplex protocol with granularity of a bit. That gives the invention all the characteristics set out in the issue to be addressed.
The method used by the invention to alternate the transmission of data between the two transmission/reception devices may be translated into “logical level multiplexing”.